1. Field of the Invention
The present invention relates to the field of prosthetic medical devices for implantation into a patient and more particularly refers to a valve assembly configured to be intraluminaly delivered into a lumen of a vessel of a patient and assembled at a location into the lumen where a native valve of the patient is deficient.
2. Description of the Prior Art
It has been a practice to open the thorax of a patient when a defective corporeal valve had to be repaired. Particularly in cardiac valves, the traditional surgery has been a very risky procedure involving the steps of opening the thorax, providing extracorporeal blood circulation, and surgically opening the heart to remove the defective valve and implanting a new one, namely a prosthetic valve generally sutured into the blood vessel having the deficient natural or native valve.
In the last years, a less risky and less invasive technique has consisted of delivering a prosthetic valve into the blood vessels of the patient and implanting the new valve at the desired location, and implanting the new prosthetic valve directly onto the native defective one. Some prosthetic valves for transluminal delivery are disclosed in several documents. U.S. Pat. No. 5,370,685 discloses a prosthetic valve comprising a flexible cylindrical sleeve with three cusps that are shown free to move in a direction to permit the blood flow and capable of moving in an opposite direction to prevent back-flow. The sleeve is fixed at a bottom edge thereof to a mounting ring made of a self-expanding structure to expand, upon release of any external pressure, to rest against a vascular wall. In order to be anchored in the wall, the mounting ring is provided with mounting pins to fix the valve at the designated valve situs.
The above described valve is of the type that are directly anchored in the vessel wall by means of any anchoring means such as hooks, pins and the like. This direct fixation while simple is still capable of being improved to prevent migration and misplacing of the valve. A cardiac valve must be fixed at the correct place and properly anchored in place to resist the constantly changed vessel diameter and turbulent blood flow.
To solve at least some of the problems of insecure fixation another type of prosthetic valve is comprised of a valve and a support structure or stent that is fixed against the vessel wall along a larger area of the vessel wall. U.S. Pat. No. 7,329,278 discloses a valve comprising a support stent or armature made of shape memory material, and configured to expand against the vessel wall and anchor therein. The armature is made of wire and has a general cylindrical shape with a central support band for placing against a vessel annulus and end portions for placing above and below the annulus, respectively. The valve also comprising the valve leaflets made of biological material (preserved human or animal valve leaflets) or of synthetic material, such as a polymer. The leaflets are fixed at their base to the central band of the armature or stent and the cusps of the leaflets are fixed to the armature through commissure points. In other words the upper part of the leaflets are fixed, by suture, for example, to the armature. In movement of opening and closing the vessel to permit/prevent the blood flow, the leaflets pull from the commissure, when closing, and impact against the armature, when opening, this causing the failure of the valve along the millions of cycles along the life time.
For a correct implantation of the valve, the same must be placed exactly at the vessel annulus and in a manner to guarantee no leaks. The annulus is, some times, calcified therefore it does not offer e proper set for the new valve. The valves of the type that the support ring thereof is directly anchored at the annulus must be placed adequately in order to accommodate to the annulus. If misplaced, migration is to be expected.
In the valves employing a self expandable stent support, such stent support needs to be very long to prevent migration. Thus the self expandable stent inconveniently protrudes into the ventricle and into the first segment of the aorta. Distinct from this, the valves with balloon expandable stent support are shorter because the anchorage is better and migrations seems to be less frequent. However, with a balloon expandable stent support a damage to the valve leaflets is to be expected because the leaflets are mounted into the stent and when the stent is expanded by the balloon, the leaflets, made of flexible synthetic or natural tissue and placed between the balloon and the stent, will be squeezed against the stent by the balloon exerting the necessary radial expanding force, during inflation.
In addition to the foregoing, the flexible valve material, natural tissue or synthetic, is directly fixed to the stent in a manner that upper points of the flexible leaflets are fixed to the stent. These anchoring points, made by suturing for example, are continuously subject to concentrated stress each time the leaflets move to a close position.
Under the above circumstances it would be very convenient to have a new valve assembly with the advantages of the valves having a stent, thus improving the anchoring of the valve assembly in the vessel wall but without the drawbacks of these conventional valves relating to the stress of the commissure points where the material of the valve leaflets fail under fatigue stress by cycling pulling effect as well as without the drawbacks of the known intraluminaly-delivered valves having the leaflets material compressed and probably damaged when remaining between the outer support stent and the balloon expanding the assembly to anchor it in the vessel.